A Study on the effect of Zeta potential on coagulation process in water treatment

Abstract

Turbidity is considered one of the most important problems of drinking water and it is usually treated with water containing molecules, of plankton and colloids through the process of coagulation and flocculation. And coagulants most commonly used in the water treatment process are aluminum sulfate (alum), ferric chloride,Poly aluminum chloride, which was recently discovered to have negative side effects on human health if are not taken into account the amount and weights added to water and allowed rates. This research aims to study the possibility of controlling the physical function of " Zeta potential " through the study of its impact on the process of coagulation/flocculation of plankton and colloids in the water and causing turbidity in order to minimize the use of chemicals in water treatment processes. The study consists of two phases The first is the comparison between the three efficiency coagulations .The most efficient of them was chosen in terms of its ability to remove the turbidity of the water and meet standard specifications for drinking water. and second phase consists comparing the coagulant that has been chosen in the first phase with the high-voltage capacitor (Zeta Rod) to study the impact of this technology on the coagulation process by applying a high DC voltage (5 kV to 30 kV) to the turbid waters samples. Experiments were conducted by on samples of water whose turbidity was controlled from through the addition of Alkaúolin coagulants remove was evaluated using the jar test. The tests were carried out at three levels of turbidity 580 , 150, 50 NTU. The results show superiority of poly aluminum chloride over alum and ferric chloride to remove turbidity, It was found that a dose of 75 mg / l of this coagulant is able to reduce the turbidity of the water from 580 to 4.5 NTU that is, removal efficiency of (99.2%) which conforms to the specification of water of the Iraqi standard for drinking water, The same dose was able to reduce the turbidity of 150 NTU to 1.14 (99.24%) and 50 to 1.51 NTU (96.9%) in the same operating conditions and testing. While the efficiency of removal of turbidity for each of alum and ferric chloride in the same dose and operational conditions by (98.5%) and (98.8%) of the level of turbidity of 580 NTU and (95.6%) and (97.4%) of the level of turbidity of 150 NTU and (93.5%) and (85.6%) to the level of turbidity of 52 NTU, respectively. The results of the second phase which is the focus of this research show that after the use of high voltage capacitor technology and the application of high DC voltage ranging from 5 kV to 30 kV, the levels of turbidity of the water increased over those when using the same values doses used in the first phase of the coagulant poly aluminum chloride and under the same operating conditions. which indicates that there is a separation process for plankton and clays because of these voltages applied, which in turn affects the physical function of" Zeta potential" , that is, it charges formed on the surfaces of plankton and clays particles resulting in increased turbidity levels. This means that with these values of voltages ranging from 5 to 30 kV DC using a technique of (Zeta Rod) there will be no enhance for the process of coagulation, but there will be a separation of particles of larger of clays, plankton and this property could be used in systems of water treatment and so-called systems of reverse osmosis(RO)to increase the efficiency of filters and membranes used.